This invention relates generally to semiconductor manufacture and specifically to an improved interconnect for electrically engaging semiconductor components such as dice, packages, wafers, panels, boards, and electronic assemblies containing dice or packages.
Different types of semiconductor components include terminal contacts which provide electrical connection points for applying electronic signals to the integrated circuits contained on the components. For example, bare dice and semiconductor wafers typically include bond pads which function as terminal contacts. Chip scale packages typically include solder balls, which function as terminal contacts. Electronic assemblies, such as circuit boards and field emission displays, can include pads, solder balls or pins which function as terminal contacts.
Typically, an interconnect must be provided for making electrical connections to the terminal contacts on the contacts. For example, semiconductor test systems include an interconnect that makes temporary electrical connections with the terminal contacts on the components. Depending on the system, the interconnect can be die sized, or wafer sized. U.S. Pat. No. 5,686,317 entitled xe2x80x9cMethod For Forming An Interconnect Having A Penetration Limited Contact Structure For Establishing A Temporary Electrical Connection With A Semiconductor Diexe2x80x9d, describes a die level interconnect configured for use with a carrier. U.S. Pat. No. 5,869,974 entitled xe2x80x9cMicromachined Probe Card Having Compliant Contact Members For Testing Semiconductor Wafersxe2x80x9d, describes a wafer level interconnect configured for use with a wafer prober.
Interconnects are also used to provide permanent electrical connections to a semiconductor component for various electronic assemblies. For example, U.S. Pat. No. 5,578,526 entitled xe2x80x9cMethod For Forming A Multi Chip Modulexe2x80x9d, and U.S. Pat. No. 5,789,278 entitled xe2x80x9cMethod For Fabricating Chip Modulesxe2x80x9d, describe multi chip modules having interconnects which form permanent electrical connections to the terminal contacts on components.
One material that can be used to fabricate interconnects is silicon. Silicon can be used as a substrate material, and also to form contacts for the interconnect. With silicon, a coefficient of thermal expansion (CTE) of the interconnect matches the CTE of the component. In test systems, the matching CTEs minimize thermal stresses during test procedures, such as burn-in, which are conducted at elevated temperatures. In electronic assemblies, the matching CTEs minimize thermal stresses due to heat generated by the semiconductor component, or by the operating environment.
One aspect of silicon is that it is a semiconductor material, and does not have sufficient electrical conductivity to permit signal transmission. Accordingly, the silicon must be coated with electrically conductive materials to form contacts, conductive traces and bond pads for the interconnect. The conductive materials can include metals, such as copper and aluminum, or metal suicides, such as TiSi2.
Some of the conductive materials used in interconnects do not possess sufficient strength to resist deformation during fabrication or use of electronic assemblies. For example, in test systems, some conductive materials, such as metals, are prone to wear and oxidation with continued usage. Also, some conductive materials, such as metal silicides, do not possess a thermal conductivity which permits efficient heat dissipation from the component.
In accordance with the present invention, an improved interconnect for semiconductor components, and a method for fabricating the interconnect are provided. The interconnect comprises a substrate, and a pattern of interconnect contacts on the substrate configured to electrically engage component contacts on the components.
In an illustrative embodiment, the substrate comprises silicon, and the interconnect contacts comprise silicon projections, or alternately indentations in the substrate, at least partially covered with silicon carbide (SiC) layers. The interconnect also includes a pattern of conductors (conductive traces) in electrical communication with the silicon carbide layers, and a pattern of terminal contacts, such as bonding pads, in electrical communication with the silicon carbide layers. The conductors provide electrical paths for signal transmission to and from the interconnect contacts. The terminal contacts provide an electrical connections points for external circuitry, such as test circuitry to the interconnect.
As silicon carbide has a mechanical hardness similar to diamond, the silicon carbide layers provide a wear-resistant surface for the interconnect contacts. The wear resistant surface makes the interconnect particularly suitable to testing applications wherein the interconnect contacts are used to perform multiple test procedures on many different components. The silicon carbide layer also has a relatively high strength and a high maximum working temperature, such that the interconnect contacts can resist deformation at temperature.
In addition, as silicon carbide has a high thermal conductivity, the silicon carbide layers provide efficient heat transfer from the component contacts to the interconnect contacts, and better temperature control at the interface of the interconnect contacts with the component contacts. Further, the silicon carbide layers can be configured to substantially cover the area on the substrate between the interconnect contacts to provide a large surface area for dissipating heat generated by the component.
Although silicon carbide has a relatively low electrical conductivity, a sufficient electrical conductivity can be provided by doping a silicon carbide layer with selected dopants having either a P-type, or a N-type conductivity. Doping can be accomplished during CVD deposition of silicon carbide, or following deposition by implanting the dopants (e.g., ion implantation) and then annealing to activate the dopant. Electrical conductivity can also be provided by oxidation of the silicon carbide conductive layers using localized thermal heating. One method for performing the localized thermal heating is with a focused laser beam. Using a doping or oxidation process, the interconnect contacts can have an electrical conductivity similar to contacts covered with a metal.
Preferably, the conductors on the interconnect are fabricated from a highly conductive metal, such as aluminum or copper, to provide low resistance signal paths for the interconnect contacts. In addition, conductive vias and backside contacts can be formed on the substrate in electrical contact with the conductors, or directly with the silicon carbide conductive layers.
Alternately, rather than forming the conductors of a separate metal, a blanket deposited silicon carbide layer can be patterned to provide the silicon carbide conductive layers, as well as the conductors for the interconnect contacts. In this case a circuit side surface of the interconnect is substantially covered with silicon carbide, such that the interconnect possesses improved heat dissipation characteristics. As another alternative, a blanket deposited silicon carbide layer can be selectively doped to form the silicon carbide conductive layers, and a separate metallization process can be used to form conductors on the blanket deposited silicon carbide layer.
The interconnect can be configured for die level testing of discrete components, such as bare dice or chip scale packages, or alternately for wafer level testing of multiple components contained on a common substrate, such as a wafer, a panel, a circuit board, or an electronic assembly. In addition, the interconnect contacts can be configured to electrically engage either planar component contacts (e.g., bond pads, test pads, land pads), or bumped component contacts (e.g., solder balls, metal bumps, conductive polymer bumps). For engaging planar component contacts, the interconnect contacts can comprise etched members with projections for penetrating the component contacts to a limited penetration depth. For engaging bumped component contacts, the interconnect contacts can comprise projections configured to penetrate the bumped component contacts, or alternately recesses sized and shaped to retain the bumped component contacts.
For a die level test system, the interconnect is configured for assembly in a testing apparatus, such as a carrier, configured to retain one or more components in electrical communication with testing circuitry. The testing apparatus includes a base on which the interconnect is mounted, and a force applying mechanism for biasing the components against the interconnect. For a wafer level test system, the interconnect is configured for use with a wafer testing apparatus such as a wafer prober. In the wafer level test system the interconnect can take the place of a conventional probe card.
The interconnect can also be configured to make permanent electrical connections with components for constructing electronic assemblies, semiconductor packages, and multi chip modules.
The method for fabricating the interconnect, broadly stated, includes the steps of: providing a substrate, forming interconnect contacts on the substrate, forming an insulating layer on the substrate and on the interconnect contacts, forming silicon carbide conductive layers on the interconnect contacts and on select portions of the substrate, and then forming conductors and terminal contacts in electrical communication with the silicon carbide conductive layers.
The silicon carbide conductive layers can be deposited on the interconnect contacts by chemical vapor deposition through a mask, or by conformal deposition of a layer of silicon carbide on the substrate followed by etching. Also, the silicon carbide conductive layers can be doped during deposition, or implanted following deposition. Alternately, the xe2x80x9cas depositedxe2x80x9d silicon carbide conductive layers can be subjected to localized heat with a laser beam to improve the electrical conductivity of the interconnect contacts. A silicon carbide layer can also be deposited, or patterned, to form the conductors and the terminal contacts as well as a large area heat transfer surface on the interconnect.